Am Nat. 2019 Feb;193(2):213-226. doi: 10.1086/701434. Epub 2019 Jan 10.
Niche and fitness differences control the outcome of competition, but determining their relative importance in invaded communities-which may be far from equilibrium-remains a pressing concern. Moreover, it is unclear whether classic approaches for studying competition, which were developed predominantly for pairs of interacting species, will fully capture dynamics in complex species assemblages. We parameterized a population-dynamic model using competition experiments of two native and three exotic species from a grassland community. We found evidence for minimal fitness differences or niche differences between the native species, leading to slow replacement dynamics and priority effects, but large fitness advantages allowed exotics to unconditionally invade natives. Priority effects driven by strong interspecific competition between exotic species drove single-species dominance by one of two exotic species in 80% of model outcomes, while a complex mixture of nonhierarchical competition and coexistence between native and exotic species occurred in the remaining 20%. Fungal infection, a commonly hypothesized coexistence mechanism, had weak fitness effects and is unlikely to substantially affect coexistence. In contrast to previous work on pairwise outcomes in largely native-dominated communities, our work supports a role for nearly neutral dynamics and priority effects as drivers of species composition in invaded communities.
生态位和适合度差异控制着竞争的结果，但在远离平衡的入侵群落中确定它们的相对重要性仍然是一个紧迫的问题。此外，经典的竞争研究方法主要是针对相互作用的两个物种发展起来的，这些方法是否能完全捕捉到复杂物种组合中的动态变化还不清楚。我们使用草原群落中两种本地种和三种外来种的竞争实验来参数化一个种群动态模型。我们发现本地种之间的适合度差异或生态位差异很小，导致替换动态缓慢和优先效应，但外来种的巨大适合度优势使其可以无条件入侵本地种。由外来物种之间强烈的种间竞争驱动的优先效应导致在 80%的模型结果中，两种外来物种中的一种占据了单一种群的主导地位，而在剩余的 20%中，出现了非等级竞争和本地种与外来种共存的复杂混合。真菌感染是一种常见的共存机制，但其对适合度的影响较弱，不太可能显著影响共存。与之前在主要由本地种主导的群落中对成对结果的研究相比，我们的工作支持近中性动态和优先效应作为入侵群落中物种组成的驱动因素的作用。
